The value of electrophoresis in clinical chemistry has been recognized for some time in the analysis, for example, of proteins in serum as well as other body fluids. Typically, gel electrophoresis is the method of choice in clinical chemistry laboratories. With gel electrophoresis, a sample is applied near one edge of a layer of gelatin carried on a flexible sheet, usually called a "gel". The gel is electrophoresised, stained and the density of the resulting pattern is measured to reveal the proteins contained in the sample. Although gel electrophoresis is relatively inexpensive in terms of the supplies and equipment required to perform sample analyses, the technique requires skilled technicians and is time consuming, effectively resulting in a high price per test and limiting the number of tests that can be performed using the technique.
Efforts have been made to automate electrophoresis in the clinical laboratory. For example, U.S. Pat. No. 4,124,470 to Dahms describes a zone electrophoresis apparatus where a number of samples in individual large-bore tubes can be processed serially on a turntable. Although this apparatus automates the electrophoresis process, it requires large volumes of electrophoresis reagents, such as buffer and the like, and the use of wicks and membranes as part of the electrophoresis circuit.
Capillary electrophoresis is a more recent development and can be used to perform the type of electrophoretic separations presently performed with gels. In capillary electrophoresis, a small tube or capillary having an inside bore diameter in the range of about five microns to about two hundred microns and often about twenty cm long is filled with an electrically conductive fluid, or buffer. A small quantity of a sample to be analyzed is introduced into one end of the capillary bore and the ends of the capillary are placed into separate reservoirs of buffer. A direct current voltage in a range of about 2,000 volts to about 30,000 volts is applied to the ends of the capillary by means of electrodes positioned in the buffer reservoirs, causing a small current, typically in the range of about five microamps to about one milliamp, to flow through the capillary.
With the correct polarity applied across the capillary, the sample begins to migrate from the sample introduction end toward the other end of the capillary. As this migration occurs, different molecules in the sample travel at different rates primarily because of slightly different electrical charges on the molecules. These different migration rates cause molecules with slightly different charges to separate one from the other, some moving more quickly and advancing relatively with respect to more slowly moving molecules. As the sample nears the other end of the capillary, the small volume of sample becomes separated into bands of different molecules according to the relative migration rates of the molecules. These bands or groups of different molecules are detected near the other end of the capillary by, for example, passing a light beam through the bore of the capillary. Changes to the light beam, such as absorbance caused by the different molecules, are detected as the separated molecules pass through the beam, thus identifying the different molecules or the classes or categories of molecules in the sample and the relative concentration of such molecules.
Automated forms of capillary electrophoresis analyzers are known in the art. For example European Patent Application number 89302489.3, publication number 0,339,779 A2, corresponding to U.S. patent application Ser. No. 188,773, filed Apr. 29, 1988 (Burolla) describes an automated capillary electrophoresis apparatus. That apparatus includes two conveyors for positioning vials under ends of a capillary mounted in a cartridge. The ends of the capillaries along with electrodes are inserted into the vials by means of hypodermics that pierce caps on the vials. A single detector provides detection of electrophoresised samples.
Another automated capillary electrophoresis apparatus is described in U.S. Pat. No. 5,045,172 to Guzman. The Guzman apparatus includes two rotating tables at opposite ends of the apparatus that hold sample and buffer cups. A capillary, which is described in Guzman as being a single capillary or a plurality of capillary tubes operated in parallel or in a bundle, has two opposite ends. These ends are positioned by automated arms and posts in respective corresponding pairs of cups to first draw sample into the capillary and to then electrophorese the sample. As with Burolla, a single detector is used to detect the results.
Neither of the automated analyzers just described, however, is suitable for routine clinical laboratory applications. Each of such analyzers requires considerable manual manipulation despite their automated nature, such as preparing and placing individual sample and buffer vials onto the analyzer, programming the analyzer for the various analytical routines, and the like. Because only one sample can be electrophoresed and detected during each analysis cycle of the analyzers, the number of samples per unit time, or throughput, is severely restricted as compared to the needs of most routine clinical laboratory work.
Yet another disadvantage of the Guzman analyzer is that it appears difficult to replace the capillary. While the capillary in Burolla is easy to replace because it is contained within a cartridge, the Burolla cartridge adds expense to the use of the analyzer. Further, the commercial version of the Burolla analyzer (available from Beckman Instruments, Inc., Fullerton, Calif. U.S.A. under the trademark P/ACE) requires an external high-pressure nitrogen tank, adding to the expense and inconvenience of use of the analyzer in a clinical chemistry environment.
Thus, there is a need for an automated capillary electrophoresis analyzer that is easy to use, requires less sample manipulation, is relatively inexpensive, and is capable of substantially increased throughput as compared to prior capillary electrophoresis analyzers. There is also a need for an automated capillary electrophoresis analyzer that can be easily adapted for use in a clinical chemistry laboratory.